COMMUNITY FORUM

Weight bearing capacity of wood beams

We are rebuilding our front stairs, which requires a permit. The permit people, being so helpful, told me I needed to hire an engineer to draw my plans. So that the calculations proving the wood framing will hold the concrete are there. (the previous set of stairs lasted 50 years and we are using wood twice as thick) The stairs are 4' wide, each stair has a rise of 7" and a run of 10". The treads (2 X 11 X 48) are attached to the stringers (the risers are the same wood 1" thick) The stringers (4 of them) are 2 X 12 X 100 before the cutouts were done. They are attached to 2 X 4 existing beams set 12 inches apart down the stairs and 13 inches apart under the porch. I know how much the concrete (1" thick) weighs, I need to know the weight capacity of the wood. It is pressure treated lumber from Home Depot. I'm good at math so if there is a formula I can run with that.